The present invention relates to a four-point contact ball bearing, for example, used in an electromagnetic clutch, a pulley, etc. in an automobile air conditioner.
In a four-point contact ball bearing of this type, both the curvature radius of a raceway groove of an outer ring and the curvature radius of a raceway groove of an inner ring have been heretofore selected to be 52% of the diameter of each ball to thereby enlarge a contact ellipse between the ball and each of the raceway grooves to prevent resisting moment and peeling. The four-point contact ball bearing has advantages in reduction in weight, size and cost.
In the related-art four-point contact ball bearing, however, the contact area of each ball with the raceway grooves of the inner and outer rings increased because both the curvature radius of the raceway groove of the outer ring and the curvature radius of the raceway groove of the inner ring were selected to be 52% of the diameter of the ball. Hence, there was a problem that heat generated due to sliding was apt to cause burning. Particularly when the four-point contact ball bearing is used in a pulley bearing, an electromagnetic clutch, etc. in an automobile air conditioner, the temperature of the inner ring has a tendency to rise because heat is transmitted to the inner ring from a boss of a compressor. If the temperature of the outer ring is reduced, heat-radiating characteristic is improved. Hence, how to improve the heat-radiating characteristic of the outer ring is the important point for preventing burning.
If both the curvature radius of the groove of the outer ring and the curvature radius of the groove of the inner ring were selected to be equal to 52% of the diameter of the ball in the same manner as in the related-art example, the contact pressure of the raceway groove of the inner ring with the ball became larger than the contact pressure of the raceway groove of the outer ring with the ball because the sectional shape of the raceway groove of the inner ring perpendicular to the axis of the bearing was convex to the ball whereas the sectional shape of the raceway groove of the outer ring perpendicular to the axis of the bearing was concave to the ball. As a result, the contact pressures were unbalanced. Hence, there was also a problem that the peeling life of the ball bearing was shortened.
Further, in the related-art four-point contact ball bearing, each of the raceway grooves of the inner and outer rings was generally formed so as to come into contact with the balls laterally symmetrically with respect to the widthwise center of the raceway groove. Hence, when load was applied on each ball in the condition that the value of offset with respect to the axial centers (i.e., the value of displacement in axial center position between the raceway grooves of the inner and outer rings) was zero, spin was not generated because the ball rotated only in a direction of the circumference of each raceway groove. For this reason, failure in grease supply might occur partially, so that failure in lubrication occurred and resulted in premature burning.
In detail, in FIG. 4, when load is applied on each ball 53 in the condition that the value of offset is zero, the ball 53 decides an axis R parallel with the axial direction of the bearing as its own rotation axis with the rotation of the outer ring 51 or the inner ring 52 so that the ball 53 revolves around the axial center of the bearing on the raceway grooves 51a and 52a while rotating on its own axis R without generation of spin making the ball 53 rotate on its rotation axis inclined with respect to the axial direction of the bearing. For this reason, grease circulated, for example, as represented by the arrow in FIG. 3 with the rotation of the ball 53, etc., so that grease did not go toward the center portion of the ball 53 surrounded by contact points S, T, U and V at which the ball 53 came in contact with the raceway grooves 51a and 52a. As a result, failure in grease supply might occur between the center portion of the ball 53 and each of the outer and inner rings 51 and 52 and a cage 54, so that failure in lubrication occurred and resulted in premature burning.
Therefore, an object of the invention is to provide a four-point contact ball bearing which is so excellent in heat-radiating characteristic that burning hardly occurs and which is hardly peeled. Another object of the invention is to provide a four-point contact ball bearing in which failure in lubrication can be prevented to make the life of the ball bearing long even in the case where load is applied on each ball in the condition that the value of offset with respect to the axial centers of raceway grooves is zero.
In order to solve the aforesaid object, the invention is characterized by having the following arrangement.
(1) A four-point ball bearing comprising:
an inner ring and an outer ring defining raceway grooves, respectively, each of the raceway grooves being constituted by two circular arcs different in curvature provided on opposite sides of a widthwise center of the raceway groove; and
a plurality of balls arranged between the inner and outer rings so that the balls can roll,
wherein in at least one of the raceway grooves, a center of curvature of one of the circular arcs and a center of curvature of the other circular arc are displaced from each other at least in a radial direction so that spin is generated in each of the balls.
(2) The four-point contact ball bearing according to (1), wherein each of the balls comes into contact with the raceway groove of the inner ring at two points and comes into contact with the raceway groove of the outer ring at two points.
(3) The four-point contact ball bearing according to (2), wherein a curvature radius of the raceway groove of the outer ring is selected to be larger than a curvature radius of the raceway groove of the inner ring.
(4) The four-point contact ball bearing according to (3), wherein the curvature radius of the raceway groove of the inner ring is selected to be in a range from 50.5% to 53.5% of a diameter of the ball, and the curvature radius of the raceway groove of the outer ring is selected to be larger by 2% to 6% of the diameter of the ball than the curvature radius of the raceway groove of the inner ring.
(5) The four-point contact ball bearing according to (3), wherein the curvature radius of the raceway groove of the outer ring is selected to be in a range of from 55% to 56.5% of a diameter of the ball.
(6) A four-point contact ball bearing comprising:
an inner ring and an outer ring defining raceway groove, respectively; and
a plurality of balls arranged between the inner and outer rings so that the balls can roll, each of the balls comes into contact with the raceway groove of the inner ring at two points and comes into contact with the raceway groove of the outer ring at two points,
wherein a curvature radius of the raceway groove of the outer ring is selected to be in a range from 55% to 56.5% of a diameter of the ball.
(7) A four-point contact ball bearing comprising:
an inner ring and an outer ring defining raceway groove, respectively; and
a plurality of balls arranged between the inner and outer rings so that the balls can roll, each of the balls comes into contact with the raceway groove of the inner ring at two points and comes into contact with the raceway groove of the outer ring at two points,
wherein a curvature radius of the raceway groove of the inner ring is selected to be in a range from 50.5% to 53.5% of a diameter of said ball, and a curvature radius of the raceway groove of the outer ring is selected to be larger by 2% to 6% of the diameter of the ball than the curvature radius of the raceway groove of the inner ring.